“I have a number of regrets about this sad situation,” said Heyman, an ex-Marine who has headed the prestigious institution for just four months. Michael Heyman said in describing how the Smithsonian became embroiled in a yearlong controversy that not only questioned the museum’s intentions but caused a slump in museum funding. “We made a basic error,” Smithsonian Secretary I. In a victory for World War II veterans, the Smithsonian Institution backed down Monday from plans to commemorate the first use of the atomic bomb with an exhibit that critics charged would portray the United States as heartless aggressors at the close of the war against Japan.